When an iron series material such as steel is used as a sliding member, it has conventionally been known that an organic molybdenum lubricating oil additive such as molybdenum dithiocarbamate (MoDTC) which is a friction reduction agent exhibits low friction properties when it is added to a lubricant.
Here, in a lubricant (for example, engine oil) actually used in industry, various additives are contained. For example, an extreme pressure agent represented by zinc dialkyldithiophosphate (ZnDTP) or a detergent-dispersant forms a lubricating film at the sliding surfaces as in the lubricant. Therefore, the lubricating oil to which an organic molybdenum lubricating oil additive has been added cannot sufficiently form a lubricating film at the sliding surfaces.
That is, various kinds of additives other than the additives for the lubricating oil compete for forming the lubricating film, so that even when the organic molybdenum lubricating oil additive is added, there are cases where the effects cannot be obtained or the effects cannot sufficiently be exhibited.
In particular, since diesel engine oil contains a detergent-dispersant with a large amount, the phenomenon markedly generates that the effects cannot be obtained or the effects cannot sufficiently be exhibited, although the organic molybdenum lubricating oil additive is added,
As the other prior art, for example, a technique in which zinc dialkyl dithio compound and a lubricant are mixed has been proposed (see Patent Literature 1).
However, an object of such a prior art is to reduce the friction coefficient in the range of a low to medium temperature, and it does not intend to solve the above-mentioned problems.